This invention relates generally to sensing devices and more particularly to sensing devices which use inorganic chemical salt compositions that change color in response to changes in certain conditions such as humidity so that a visual representation of such humidity conditions are indicated.
A number of sensing devices have been proposed which utilize inorganic chemical salt compositions that change color in response to changes in certain conditions such as relative humidity. Examples of such devices which utilize inorganic chemical salt compositions to sense changes in relative humidity are illustrated in U.S. Pat. Nos. 2,249,867 and 3,680,364. These types of such prior art sensing devices have a common problem in that it is relatively difficult to visually perceive changes in the color of the inorganic chemical salt compositions in response to small changes in the relative humidity being sensed. Another problem associated in the manufacture of such prior art sensing devices is the difficulty in insuring that the inorganic chemical salt compositions are distributed uniformly throughout the visual area of the device to insure adequate representation of the changes in humidity. Yet another problem associated with such prior art devices is that, when the dispersed inorganic chemical salt compositions are exposed to water in liquid rather than vapor form, the moisture tended to leach the salt compositions out of the carrier material so that the device loses its humidity sensing capability.